1. Field of the Invention
This invention relates in general to casing seals for wellheads, and in particular to a metal seal for sealing between the casing and the wellhead bore.
2. Description of the Prior Art
In a completed oil or gas well, one or more strings of casing will be cemented in the well. A wellhead locates at the surface for supporting the upper end of the casing. In subsea wells, typically a casing hanger will be secured to the upper end of a string of casing.
The casing hanger is an annular member that has an outer surface machined for forming a seal. A casing hanger seal will locate between the casing hanger and the wellhead to seal the annular space surrounding the casing. In many cases, the casing hanger seal will be metal.
Occasionally, difficulties will be encountered in running the string of casing. If the casing cannot extend to the full depth of the well, then it may be impossible to secure a casing hanger to the upper end of the string. When this happens, an emergency seal must be used to seal the annular space between the casing hanger and the wellhead.
Sealing against casing is much more difficult than sealing against a casing hanger. The casing will have a rough exterior. In U.S. Pat. No. 4,911,245, Adamek, et al, Mar. 27, 1990, sealing for a surface wellhead against casing utilizes a member with deformable bands. An inlay of soft material locates in cavities between the bands. While workable, improvements are desirable.